Ball Grid Array (BGA) packaging is an Integrated Circuit (IC) packaging technology. Therein, a chip is disposed inside the package and the package is electrically connected to the Printed Circuit Board (PCB) through a plurality of solder balls. Solder balls are disposed on the corresponding external contact pads disposed on the bottom surface of the substrate of the Ball Grid Array package. Therefore, the Ball Grid Array package has more external I/O pins, shorter wiring distance and faster signal transmission when compared to the conventional Dual Inline Package (DIP).
As shown in FIG. 1 and FIG. 2, a conventional Ball Grid Array package 20 includes a substrate 30, a chip 40 and an encapsulant 50. The chip 40 is disposed on the upper surface 31 of the substrate 30. The encapsulant 50 is formed over the upper surface 31 of the substrate 30 to encapsulate the chip 40. A plurality of external contact pads 33 and a circuitry 34 are disposed on the bottom surface 32 of the substrate 30 before performing a BGA packaging process. Additionally, the circuitry 34 and the ball pads 33 are formed in a same metal layer in the substrate 30 for signal transmission. A plurality of solder balls 35 are disposed on the external contact pads 33.
As shown in FIG. 1 and FIG. 2 again, a chip projective area 32a is defined inside the bottom surface 32 of the substrate 30 by projecting the edges of the chip 20 from the upper surface 31 to the opposing bottom surface 32. The circuitry 34 is located outside some outermost external contact pads 33 positioned in the specific area of the chip projective area 32a so that the circuitry 34 is most vulnerable to thermal stress. During thermal cycling reliability test, the circuitry 34 is easily cracked due to thermal stress concentration leading to package failure.